Early draft of VAccordionArchiveFile

src/main/java/sh/shh/midi/roland/VAccordionArchiveFile.java

@@ -0,0 +1,90 @@
+package sh.shh.midi.roland;
+
+import org.w3c.dom.Document;
+import org.xml.sax.InputSource;
+import org.xml.sax.SAXException;
+
+import javax.xml.parsers.DocumentBuilder;
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.parsers.ParserConfigurationException;
+import javax.xml.transform.Transformer;
+import javax.xml.transform.TransformerException;
+import javax.xml.transform.TransformerFactory;
+import javax.xml.transform.dom.DOMSource;
+import javax.xml.transform.stream.StreamResult;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.StringReader;
+import java.io.UTFDataFormatException;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Path;
+import java.util.Arrays;
+
+public class VAccordionArchiveFile {
+    private final DocumentBuilder xmlBuilder;
+    private Document xml;
+    private InputStream stio;
+    private File file;
+
+    private VAccordionArchiveFile() {
+        try {
+            xmlBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
+        } catch (ParserConfigurationException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public VAccordionArchiveFile(String filename) throws IOException, SAXException {
+        this(new File(filename));
+    }
+
+    public VAccordionArchiveFile(File file) throws IOException, SAXException {
+        this(new FileInputStream(file));
+        this.file = file;
+    }
+
+    public VAccordionArchiveFile(InputStream stio) throws IOException, SAXException {
+        this();
+        this.stio = stio;
+        String xmlData = extractXmlString();
+        xml = xmlBuilder.parse(new InputSource(new StringReader(xmlData)));
+    }
+
+    public String getFilename() {
+        return file.getName();
+    }
+
+    public Path getPath() {
+        return file.toPath();
+    }
+
+    public Document getXml() {
+        return xml;
+    }
+
+    public void writeXml(String outputFilename) throws IOException, TransformerException {
+        writeXml(new File(outputFilename));
+    }
+
+    public void writeXml(File outputFile) throws TransformerException, IOException {
+        TransformerFactory tf = TransformerFactory.newInstance();
+        Transformer transformer = tf.newTransformer();
+        FileWriter writer = new FileWriter(outputFile, StandardCharsets.UTF_8);
+        transformer.transform(new DOMSource(xml), new StreamResult(writer));
+        writer.close();
+    }
+
+    String extractXmlString() throws IOException {
+        byte[] utf8bom = stio.readNBytes(3); // first 3 bytes are UTF-8 BOM
+        if (!Arrays.equals(utf8bom, new byte[]{(byte) 0xEF, (byte) 0xBB, (byte) 0xBF})) {
+            throw new UTFDataFormatException(String.format("Invalid VAccordion archive file; starting bytes should" +
+                    " be 'efbbbf', found '%02x%02x%02x'", utf8bom[0], utf8bom[1], utf8bom[2]));
+        }
+        int xmlDocLength = ByteBuffer.wrap(stio.readNBytes(4)).getInt(); // next 4 bytes are int length of XML file
+        return new String(stio.readNBytes(xmlDocLength), StandardCharsets.UTF_8);
+    }
+}